1. Technical Field
The present invention generally relates to a structure and method for reinforcing a semiconductor device, and more particularly, to a structure and method for preventing the cracking of a semiconductor device during thermal cycling or mechanical loading.
2. Background Art
In the production of integrated circuitry, a semiconductor device is often affixed to an organic substrate, such as an organic chip carrier having distinct material properties. For example, under present technology, the semiconductor device can be formed from silicon, gallium arsenide, or the like, whereas the organic substrate can be made from epoxy, cyanate ester or other similar base. This difference in materials comprising the components often leads to problems during fabrication and use when a semiconductor device is subject to thermal cycling. Specifically, the different materials have distinct coefficients of thermal expansion (CTE) which, upon thermal cycling, cause the bottom surface (commonly referred to as the "front" or "metalization" surface) of the semiconductor device to expand and contract at a different rate than its top surface (commonly referred to as the "back" or "free" surface). When this occurs, the flexibility of the substrate will cause the more rigid semiconductor to bend and crack resulting in failure or significant decrease in performance of the semiconductor device.
Thus, the ability of a semiconductor device to withstand the thermal cycling process is important in ensuring optimal performance of integrated circuitry.
Heretofore, many manufacturers have applied a metallic liner to a semiconductor device before mounting the device on a substrate. One such example of this is shown in U.S. Pat. No. 4,866,505 to Roberts et al., hereby incorporated by reference. Recognizing the problems associated with differing coefficients of thermal expansion, Roberts et al. teaches coating the underside of the semiconductor device with a metallic liner prior to bonding the device to the substrate. The purpose of this is to increase the area of the device that contacts the substrate as the two are bonded together. While such an embodiment may result in enhanced bonding of the device to the substrate, it will not aid in the prevention of cracking on the surface of the device and, accordingly, device performance will continue to suffer.
Therefore, there exists the need for a reinforced semiconductor device that will not crack or otherwise become defective upon thermal cycling.